1. Field of the Invention
This invention pertains to telecommunications, and particularly to the structure and operation of shared telecommunication networks.
2. Related Art and Other Considerations
In a typical cellular radio system, mobile user equipment units (UEs) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
One example of a radio access network is the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN). The UMTS is a third generation system which in some respects builds upon the radio access technology known as Global System for Mobile communications (GSM) developed in Europe. UTRAN is essentially a radio access network providing wideband code division multiple access (WCDMA) to user equipment units (UEs). The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM-based radio access network technologies.
As those skilled in the art appreciate, in W-CDMA technology a common frequency band allows simultaneous communication between a user equipment unit (UE) and plural base stations. Signals occupying the common frequency band are discriminated at the receiving station through spread spectrum CDMA waveform properties based on the use of a high speed, pseudo-noise (PN) code. These high speed PN codes are used to modulate signals transmitted from the base stations and the user equipment units (UEs). Transmitter stations using different PN codes (or a PN code offset in time) produce signals that can be separately demodulated at a receiving station. The high speed PN modulation also allows the receiving station to advantageously generate a received signal from a single transmitting station by combining several distinct propagation paths of the transmitted signal. In CDMA, therefore, a user equipment unit (UE) need not switch frequency when handoff of a connection is made from one cell to another. As a result, a destination cell can support a connection to a user equipment unit (UE) at the same time the origination cell continues to service the connection. Since the user equipment unit (UE) is always communicating through at least one cell during handover, there is no disruption to the call. Hence, the term “soft handover.” In contrast to hard handover, soft handover is a “make-before-break” switching operation.
The Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN) accommodates both circuit switched and packet switched connections. In this regard, in UTRAN the circuit switched connections involve a radio network controller (RNC) communicating with a mobile switching center (MSC), which in turn is connected to a connection-oriented, external core network, which may be (for example) the Public Switched Telephone Network (PSTN) and/or the Integrated Services Digital Network (ISDN). On the other hand, in UTRAN the packet switched connections involve the radio network controller communicating with a Serving GPRS Support Node (SGSN) which in turn is connected through a backbone network and a Gateway GPRS support node (GGSN) to packet-switched networks (e.g., the Internet, X.25, external networks). MSCs and GSNs are in contact with a Home Location Register (HRL), which is a database of subscriber information.
There are several interfaces of interest in the UTRAN. The interface between the radio network controllers (RNCs) and the core network(s) is termed the “Iu” interface. The interface between a radio network controller (RNC) and its base stations (BSs) is termed the “Iub” interface. The interface between the user equipment unit (UE) and the base stations is known as the “air interface” or the “radio interface” or “Uu interface”. In some instances, a connection involves both a Serving or Source RNC (SRNC) and a target or drift RNC (DRNC), with the SRNC controlling the connection but with one or more diversity legs of the connection being handling by the DRNC. An Inter-RNC transport link can be utilized for the transport of control and data signals between Source RNC and a Drift or Target RNC, and can be either a direct link or a logical link as described, for example, in International Application Number PCT/US94/12419, (International Publication Number WO 95/15665). An interface between radio network controllers (e.g., between a Serving RNC [SRNC] and a Drift RNC [DRNC]) is termed the “Iur” interface.
The radio network controller (RNC) controls the UTRAN. In fulfilling its control role, the RNC manages resources of the UTRAN. Such resources managed by the RNC include (among others) the downlink (DL) power transmitted by the base stations; the uplink (UL) interference perceived by the base stations; and the hardware situated at the base stations.
Those skilled in the art appreciate that, with respect to a certain RAN-UE connection, an RNC can either have the role of a serving RNC (SRNC) or the role of a drift RNC (DRNC). If an RNC is a serving RNC (SRNC), the RNC is in charge of the connection with the user equipment unit (UE), e.g., it has full control of the connection within the radio access network (RAN). A serving RNC (SRNC) is connected to the core network. On the other hand, if an RNC is a drift RNC (DRNC), its supports the serving RNC (SRNC) by supplying radio resources (within the cells controlled by the drift RNC (DRNC)) needed for a connection with the user equipment unit (UE). A system which includes the drift radio network controller (DRNC) and the base stations controlled over the Iub Interface by the drift radio network controller (DRNC) is herein referenced as a DRNC subsystem or DRNS. An RNC is said to be the Controlling RNC (CRNC) for the base stations connected to it by an Iub interface. This CRNC role is not UE specific. The CRNC is, among other things, responsible for handling radio resource management for the cells in the base stations connected to it by the Iub interface.
The UTRAN interfaces (Iu, Iur and Iub) have two planes, namely, a control plane (CP) and a user plane (UP). In order to control the UTRAN, the radio network application in the different nodes communicate by using the control plane protocols. The RANAP is a control plane protocol for the In interface; the RNSAP is a control plane protocol for the Iur interface; and NBAP is a control plane protocol for the Iub interface. The control plane protocols are transported over reliable signaling bearers. The transport of data received/transmitted on the radio interface occurs in the user plane (UP). In the user plane, the data is transported over unreliable transport bearers. The serving radio network controller (SRNC) is responsible for establishing the necessary transport bearers between the serving radio network controller (SRNC) and the drift radio network controller (DRNC).
It has recently been contemplated that two or more operators can share network infrastructure, e.g., share a UTRAN in a particular geographical area. In the shared network all of the UTRAN resources are shared, e.g. RNCs, node-Bs, cells, etc, and can be used equally by subscribers of both sharing operators. Using shared networks, operators can reduce the cost of network build-out. But shared networks also engender many scenarios presenting technical challenges, including scenarios where subscribers require different access rights when moving between shared networks and non-shared networks, or moving within shared networks.
Various techniques for handling access rights have been proposed generally, some of which have been suggested for third generation WCDMA networks (some having been set forth in specifications of the Third Generation Partnership Project (3GPP)). Four broad categories of such proposals, briefly discussed below, are: (1) equivalent PLMNs; (2) forbidden access areas; (3) subscriber groups (to support selective handover); and (4) roaming restriction groups (to allow roaming restrictions).
The equivalent PLMN proposal essentially involves a user equipment unit (UE) treating various PLMNs as equivalent for the purposes of handover and cell reselection. Equivalent PLMNs are described, e.g., in 3GPP TS 25.304.
Forbidden location areas are those location areas which are forbidden for a user equipment unit (UE) to access. Forbidden location areas are described, e.g., in 3GPP TS 25.304, and 3GPP TS 24.008.
The subscriber group proposals involves subscriber groups which, along with their compositions, are typically pre-agreed among operators, so that (for example) each operator knows which subscriber can be included in a particular subscriber group. For example, a first subscriber group (SG) could comprise all subscribers of a first operator, and all subscribers that have roaming agreements with that operator. Operators, and thus a subscriber group can be defined or expressed, for example, as one or more IMSI-PLMNs.
As used herein, the term “IMSI-PLMN” means the PLMN which has been extracted from the IMSI of a user equipment unit (it being kept in mind that the IMSI of many user equipment units will have the same IMSI-PLMN). The international mobile subscriber identity (IMSI) is stored in the RNC for each connected mode user equipment unit. The international mobile subscriber identity (IMSI) is received in the RNC from the core network (CN) in a RANAP COMMON ID message when a radio resource control (RRC) connection is setup. The international mobile subscriber identity (IMSI) [which comprises not more than fifteen digits] comprises three components: a mobile country code (MCC)[three digits]; a mobile network code (MNC)[two or three digits]; and a mobile subscriber identification number (MSIN). The home-public land mobile network (HPLMN) id [HPLMNid] of the user equipment unit can be extracted from the international mobile subscriber identity (IMSI). In this regard, the HPLMNid of the user equipment unit is the mobile country code (MCC)+the mobile network code (MNC).
Heretofore subscriber groups have been proposed to support selective handover. Selective handover is a technique which involves filtering out the cells that are not possible/permitted (or not preferred) for handover for a given user equipment unit, and only sending the list of allowed neighbor cells to the user equipment unit, so that the user equipment unit can measure on those cells, and send the results to the RNC. The RNC will then choose a cell to which to handover to based on the measured results. Selective handover is described, e.g., in U.S. patent application Ser. No. 09/932,447,, filed Aug. 20, 2001,, entitled “Transmission of Filtering/Filtered Information Over the Iur Interface”, which is incorporated herein by reference in its entirety.
Roaming restriction groups have been employed in GSM, but are not currently passed over any interface, nor are they described in any technical specification.
Various problems arise in implementing these proposals. One such problem is lack of uniformity or alignment of solutions for UEs in the IDLE mode on the one hand, and UEs in the CONNECTED MODE on the other hand. Within Connected Mode there are four different states: CELL_DCH state; CELL_FACH state; CELL_PCH state; and URA_PCH state. As described, e.g., in U.S. Provisional Patent Application No. 60/317,970,, filed Sep. 10, 2001, entitled “RECOVERY OF MOBILE STATION(S) IN CONNECTED MODE UPON RNC FAILURE” (which is incorporated herein by reference in its entirety), each state reflects a different level of activity.
An illustrative example of such misalignment occurs in the context of a proposal involving forbidden location areas. Such proposal requires that an IDLE mode user equipment unit (UE) perform a location update in a given area to find out whether the user equipment unit (UE) is allowed access in that area or not. Performing a location update for an IDLE mode user equipment unit (UE) requires that a radio resource control (RRC) connection be set up in the UTRAN, and signaling performed from the user equipment unit (UE) towards the core network (CN). If the user equipment unit (UE) is not allowed in the area, the user equipment unit (UE) is so informed by the core network in a location area update reject message. When the location area update reject message is received, the user equipment unit (UE) updates a location area forbidden list which the user equipment unit (UE) maintains, and the RRC connection to the UTRAN is released.
The actions taken when a CONNECTED mode user equipment unit (UE) [in the CELL_FACH state; the CELL_PCH state; and the URA_PCH state] without an updated location area forbidden list enters a forbidden area for that user equipment unit (UE) differ from the above-described actions for an IDLE mode user equipment unit (UE). The CONNECTED mode user equipment unit (UE) must perform either a cell update or a URA update in the forbidden cell, and be rejected in the UTRAN (based on a subscriber group check performed in the UTRAN, or some equivalent check based on the user equipment unit's IMSI-PLMN performed in UTRAN), after which the user equipment unit (UE) goes into IDLE mode. In the IDLE mode the user equipment unit (UE) performs a location area update in the location area towards the core network. Upon receipt of a location area update reject message, the user equipment unit (UE) updates its location area forbidden list and tries to register in a new location area.
Proposals such as the foregoing dealing with access rights in shared networks thus involve considerable signaling for the mere purpose of informing a user equipment unit (UE) that it is not allowed to operate in a particular area. Moreover, various of these proposals can also lead to a CONNECTED mode user equipment unit (UE) having its RRC connection released unnecessarily.
What is needed, therefore, and an object of the present invention, is a technique to determine access rights for a user equipment unit (UE) in a shared network context with minimal signaling overhead.